Ever now and then my laptop (the computer I'm typing on now) will shut itself down for no reason at all. Within a few seconds the screen will be completely blank. Someone mentioned to me before that it could be a virus, but I've run 2 virus scanners on it, and I've cleared 2 worms, but the problem hasn't gone away. Sometimes it'll go days/weeks without doing it, but sometimes, like yesterday/today, it'll do it several times.